SELECT
  IM.PORT_CODE AS 港コード,
  PO.PORT_NAME AS 港名,
  IM.AMT AS 入国者数,
  IM_OUT.AMT AS 出国者数,
  (IM.AMT - IM_OUT.AMT) AS 差分
FROM
  IMMIGRATION AS IM
  INNER JOIN IMMIGRATION AS IM_OUT
    ON IM_OUT.PORT_CODE = IM.PORT_CODE
    AND IM_OUT.KIND_CODE = 120
  INNER JOIN PORT AS PO
    ON IM.PORT_CODE = PO.PORT_CODE
WHERE
  IM.GROUP_CODE = 120
  AND IM.KIND_CODE = 110
  AND IM.AMT > IM_OUT.AMT
ORDER BY
  差分 DESC,
  港コード DESC